The present invention relates to a vacuum contact printing device for carrying out a printing operation in which an original is closely contacted through vacuum operation to both surfaces of a base material to be exposed and, also to an exposure apparatus and an original contact device.
Generally, in a case where a picture pattern described on a transparent original such as film or glass plate, called merely an original hereinlater, is transferred to an exposure material by utilizing a contact printing method, a vacuum contact printing method has been utilized as a high precision transferring method as disclosed, for example, in Japanese Patent Laid-open Publication No. 58-136026).
FIG. 14 shows one example of a contact printing device utilizing the vacuum contact printing method of the prior art. The contact printing device comprises a pair of frame members 3 and 3 secured by a vacuum chuck, not shown, so as to arrange originals 2 and 2 made of such as glass plate on both sides of a photosensitive base member 1, packings 4 and 4 attached to opposing surfaces of the frame members 3 and 3, a vacuum pump connected to an exhaust port 5 formed one of the frame members, a bed 6 supporting the frame members 3 and 3 in a reciprocally movable manner so as to approach or separate from the frame members with each other, and lighting sources 7 and 7 disposed on both sides of the photosensitive base member 1.
A printing method utilizing the contact printing device of the character described above is carried out in the following manner.
The photosensitive base member 1 is first positioned at a predetermined position between originals 2 and 2 and, after the positioning thereof, a pair of frame members 3 and 3 are moved in directions towards the photosensitive base member 1 to thereby clamp both the surfaces of the base member 1 by the originals 2 and 2 to seal the space between the frame members 3 and 3 by the packings 4 and 4, whereby a sealed vacuum chamber 8 is defined by the originals 2 and 2, the frame members 3 and 3 and the packings 4 and 4. The exhaust port 5 is communicated with the vacuum chamber 8 and inner air in the chamber 8 is sucked by the vacuum pump through the exhaust port 5 to create the vacuum condition in the vacuum chamber 8. As a result, as shown in FIG. 15, both the originals 2 and 2 are pressed by the atmosphere to closely contact to the photosensitive base member 1. The lighting sources 7 and 7 are then lit to print the picture pattern described on the originals 2 and 2 on the photosensitive base member 1.
However, with the conventional printing device, in case of utilizing a photosensitive base member having a large area such as shadow mask for a Braun tube and an original having a large size, there has been often caused a problem of generating vacuum contact defective portions 9 as shown in FIG. 16. Such defective portions 9 are locally generated particularly at portions near the central portion of the photosensitive base member. This adverse phenomenon is discriminated by the observation of a viewer of an interference fringe, called Newton ring, or confirmation of a transferred condition of the photosensitive base member after the picture pattern transferring process. Such defects result from the fact that, when the interia of the vacuum chamber is sucked and the pressure reduced through the exhaust port, the outer peripheral portion of the original or the photosensitive base member is quickly sucked and, hence, air is sealed at a portion near the central portion thereof, such air being hardly sucked. There is no way other than a way in which such sealed air is drawn out from the closely contacted portion of the outer periphery of the original or the base member by taking a relatively long time. Accordingly, in a case where the original and the photosensitive base member each having a large size and having good smoothness are utilized, it is extremely difficult to suck and draw out the sealed air after the outer peripheral portions of the original and the base member are once closely contacted, requiring much time, for example, several or several tens of minutes, thus resulting in a significant problem for the productivity of the device.
In order to obviate the described defects of the conventional device, much care has been paid to the original or photosensitive base member for shortening the sucking and close contacting time. For example, the contact surface of the original or base member is made finely coarse to the extent of causing no problem for the exposure. According to this method, the coarse surface portion forms a minute gap at the close contacting time and the interior air in the vacuum chamber can be sucked through the minute gap. The sucking time is reduced in accordance with the extent of the coarseness. However, in this method, a process for making coarse the surface of the original or base member is additionally required, causing another problem.